1. Field of the Invention
The present invention relates to a sewing machine comprising a casing having a lower arm, an upper arm, a column connecting these arms, and in the upper arm of which a needle bar is slidingly mounted and a thread-draw lever is mounted for rocking displacement, means for driving this needle bar and this thread-draw lever in synchronised respective alternating movements and means for guiding the thread between a feed spool and a needle carried by the needle bar, defining a path for this thread which corresponds to a portion of the path of the thread-draw lever for enabling the drive of the said thread at least in one direction of displacement of the thread-draw lever.
2. Description of the Prior Art
There has already been proposed in JP-U-61-151681 a threading system in which the thread-draw arrangement comprises a gripping opening for the thread and an incline adjacent to an entry channel to this gripping opening. This thread-draw arrangement is driven in a rocking movement in synchronism with the alternating sliding movement of the needle bar. A passage containing the path of the thread-draw arrangement is formed in the upper arm of the casing of the machine to enable exit from the casing at the gripping opening for the thread. Guide means for the thread serve to maintain a portion of this thread across the exit passage from the thread guide in the path of the incline adjacent to the entry channel in such a manner that when the thread-draw arrangement is displaced towards the thread, the incline meets the thread and makes it slide on the incline by displacing it from its path until it penetrates into the gripping opening through the entry channel. An extension disposed opposite the entry channel of the gripping opening prevents untimely exit of the thread. This thread-draw arrangement thus enables automatic introduction of the thread by the simple fact that it is guided across the exit passage of the thread guide and as a result extends transversely to its path.
If the introduction of the thread into the gripping opening of the thread guide is automatic, it is not the same for the thread guidance means directing the thread from the feed spool to the needle of the needle bar. In effect, several thread guides are disposed along the path of the thread and in particular at the narrow point where the thread changes direction to descend towards the needle. After having been guided into a horizontal guide groove along which there is disposed a thread grip, the thread leaves the groove and must be introduced into a retaining guide before being directed into a vertical groove comprising guide members into which this thread must be introduced. As a result, the threading of the thread, except in regard to the thread-draw arrangement, remains quite traditional and thus demands meticulous work necessitating in particular good eyesight on the part of the operator. Moreover, this threading also forms a source of frequent errors.
There has also been proposed a simplified threading system in U.S. Pat. No. 3,347,195, in which the feed spool for the thread is disposed against the rear face of the machine and the upper face of the casing of the machine is traversed by a transverse groove permitting guidance of the thread towards the front face, the thread grip being located along this transverse groove. The remainder of the threading is traditional, the thread having in particular to be introduced into an opening of the thread-draw lever.
It has also been proposed to try to drive the thread by a thread-draw arrangement without the thread-draw arrangement gripping the thread. By this manner of thread drive, a simple lever is sufficient, and it is no longer necessary to introduce the thread into the opening of the thread guide lever. Mechanisms of this kind are described in DE-A-1,809,863 as well as in EP-A1-0,251,633. As in the case of the other solutions mentioned above, the thread must still be passed into the thread guides on account of sharp changes of direction in the path of the thread.